This invention relates to a novel relay valve combined with a load-sensing proportion valve, and more specifically to a combined load-sensing proportion and relay valve capable of automatically adjusting the pressure applicable to the power chambers of brake actuators.
Rapid development of commercial transport by such large motor vehicles as trailer-trucks in recent years has been coupled with the introduction of faster cars to cause more and more serious traffic jams on roads. In view of this, greater safety of the vehicles, that is, a braking system more reliable in action and more stable in performance than ever, is being called for.
With these heavy-duty vehicles, service brakes of the pneumatic type prevail in which indicated braking pressure from the brake valve is conducted to the relay valve so that compressed air corresponding to the indicated pressure is supplied to the brake actuators via the relay valve. Since the axle-to-axle load ratio can vary largely according to whether the vehicle is empty or loaded, the air brake system is designed to control the indicated pressure according to the movable load the vehicle carries, or the distance between the upper portion and lower portion of the spring of the suspension and thereby adequately proportion the braking forces applicable to the individual axles, avoiding any unbalanced braking action, such as partial locking of any axle alone. In order to obtain the indicated pressure corresponding to the payload as described above, a conventional brake circuit as schematically shown in FIG. 1 (I) has, between the brake valve a' and the relay valve b', a load-sensing proportion valve c' which regulates the indicated pressure from the brake valve before the pressure is delivered to the relay valve. Also included in the circuit is a reservoir d, a power chamber e, and a slack adjuster f. However, installing the load-sensing proportion valve in the line accordingly increases the amount of air retained in the line and, inasmuch as air is a compressible medium itself, the increased air volume in the line inevitably causes a lag in response of the brake actuators to the instruction from the brake valve.